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Mechanisms of stress effects on learning and decision making in younger and older adults

MECHANISMS OF STRESS EFFECTS ON LEARNING AND DECISION MAKING
IN YOUNGER AND OLDER ADULTS
by
Nichole Renee Lighthall
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(GERONTOLOGY)
August 2012
Copyright 2012 Nichole Renee Lighthall

Stress is common in daily life and often present when making important decisions that involve risk or that require learning from the positive and negative outcomes of past choices (reinforcement-based learning). An emerging literature indicates that stress can strongly influence these types of learning and decision making, but the mechanisms of these stress effects are not yet clear. Stress affects numerous brain regions and networks involved in motivated learning and decision making including those subserving reward processing, attentional control, perception, and integration hubs for cognitive, affective, and sensory information. ❧ The first aim of this dissertation was to determine whether and how these neural networks may mediate stress effects on learning and decision making (Study 1 and Study 3). Findings from Study 1 indicated that stress affects the involvement of the dorsal striatum and anterior insula in young adults during risky decision making involving monetary reward, but stress effects are opposite for men and women. Results from Study 3 revealed that stress affects the involvement of attentional control and visual perception regions during social reinforcement learning. ❧ A second aim of this dissertation was to examine age differences the impact of stress on reinforcement learning (Study 2 and Study 3). Aging is associated with declines in reinforcement learning abilities and changes to the neural networks involved in reinforcement learning and stress response. Thus, stress may affect reinforcement learning differently in younger and older people. Given older adults' already compromised functioning in this domain, it is important to determine whether stress enhances or impairs reinforcement learning in older age. Study 2 indicated that reinforcement-based learning for positive cue-outcome associations is similarly enhanced by acute stress in younger and older adults, but Study 3 found that only younger adults had this stress-related enhancement. These mixed findings highlighted the potential importance of task difficulty, level of stress arousal, and type of reinforcement in determining when age differences in stress effects will be observed for reinforcement learning. Finally, for brain activation, Study 3 found no significant stress-by-age effects, but did find age differences during social reinforcement learning, indicative of an age-related bias for positive social feedback. In sum, this dissertation provides insight into how motivated learning and decision making are affected by short-term stress and how these stress effects may depend on age. Findings presented here provide information about young and older adults' ability to manage risk- and reward-related decisions and may inform interventions targeted at addressing age-specific cognitive vulnerabilities during stress.

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MECHANISMS OF STRESS EFFECTS ON LEARNING AND DECISION MAKING
IN YOUNGER AND OLDER ADULTS
by
Nichole Renee Lighthall
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(GERONTOLOGY)
August 2012
Copyright 2012 Nichole Renee Lighthall